Bactrim Dosing for Pediatric MRSA Pharyngitis
For pediatric MRSA pharyngitis, use trimethoprim-sulfamethoxazole (Bactrim) at 8-12 mg/kg/day based on the trimethoprim component, divided into 2 doses orally for 5-10 days.
Dosing Specifics
The recommended pediatric dose is 8-12 mg/kg/day of the trimethoprim component given in either 2 divided doses orally or 4 divided doses intravenously 1. This translates to approximately 40-60 mg/kg/day of the sulfamethoxazole component when using standard formulations 1.
Practical Dosing Examples:
- For a 20 kg child: 160-240 mg trimethoprim daily (equivalent to 1-1.5 double-strength tablets or 2-3 single-strength tablets divided twice daily) 1
- For children weighing <20 kg: Use liquid suspension dosed at 8-12 mg/kg/day of trimethoprim component 1
Important Clinical Considerations
Age Restrictions
Do not use TMP-SMX in children under 2 months of age 1. The medication is pregnancy category C/D and contraindicated in the third trimester 1.
Duration of Therapy
Treat for 5-10 days depending on clinical response 1. For pharyngitis specifically, aim for the shorter end (5-7 days) if rapid clinical improvement occurs, reserving longer courses for more severe presentations 1.
Critical Limitations
TMP-SMX should NOT be used as monotherapy for initial treatment of cellulitis because it lacks reliable activity against Group A Streptococcus 1. However, for confirmed MRSA pharyngitis (culture-proven), this is not a concern as the pathogen is identified 1.
Alternative Agents for MRSA in Pediatrics
If TMP-SMX is contraindicated or not tolerated:
- Clindamycin: 10-13 mg/kg/dose orally every 6-8 hours (maximum 40 mg/kg/day), but only if local clindamycin resistance rates are <10% 1
- Linezolid: 10 mg/kg/dose every 8 hours for children <12 years (maximum 600 mg/dose) 1
- Doxycycline: 2 mg/kg/dose every 12 hours for children ≥8 years old and ≥45 kg (avoid in younger children due to tooth staining risk) 1
Monitoring and Follow-up
- Obtain throat culture before initiating therapy to confirm MRSA and determine antibiotic susceptibilities 1
- Reassess clinical response at 48-72 hours; if no improvement, consider alternative diagnosis or resistant organism 1
- TMP-SMX resistance rates vary significantly by geographic region and institution, particularly in HIV-endemic areas where rates can be substantially higher due to prophylactic use 2
Common Pitfalls to Avoid
- Do not assume TMP-SMX covers streptococcal pharyngitis - it does not reliably cover Group A Streptococcus, so culture confirmation of MRSA is essential 1
- Check local resistance patterns - TMP-SMX resistance in MRSA can be highly variable (some clonal outbreaks show high resistance) 2
- Avoid in neonates and young infants - contraindicated under 2 months due to risk of kernicterus 1